After three lean years, the ocean off California's coast this summer is suddenly rich in nutrients, and creatures - from microscopic krill to humpback whales - are thriving anew.

But whether this abundance will continue in coming seasons or is merely a bright blip in an otherwise discouraging picture year-after-year can't be predicted, say scientists monitoring the sea's productivity. The cycles of life in the Earth's warming climate are changing.

For the time being, many species of sea birds, fish and marine mammals are flourishing, and the reason lies largely in an unexpected change in two features of the ocean: The California current, flowing down the Pacific coast from Canada to Mexico, is colder than it has been in years, and strong northwest winds have increased the upwelling of cold water from just above the sea floor to the surface.

"Cold is good, and when it comes to the ocean ecosystem, the colder that upwelling gets, the better it is for all the animals in the food chain," said Steven Ramp, an oceanographer at the Monterey Aquarium Research Institute at Moss Landing.

Others agree.

"This year there's been a striking resurgence of krill in the waters off Monterey Bay, particularly for one species that has really made a comeback from the past three years," said Baldo Marinovic, a research biologist at UC Santa Cruz who specializes in the life cycles and abundance of krill, a major food source for whales, some seabirds and many species of seals.

"Sea surface temperatures that we monitor have been the coldest since the late 1980s, and that translates all the way up the food chain," he said.

"It's bringing more and more food up into levels of the ocean where fish can feed better than they have in years," Peterson said.

For example, copepods, tiny crustaceans that live on the ocean floor, are prime nutrients for upper levels of the food chain in California's ocean waters. Their upwelling is unbelievable, Peterson said.

Russell Bradley, a biologist with the Point Reyes Bird Observatory who has monitored bird life on the Farallon Islands for 20 years, said the abundance of krill has meant a big difference in the productivity of many birds.

Cassin's auklets, small gray residents of the craggy rocks on the Farallones, failed to breed during the past three summers ago for the first time in 35 years, Bradley said, and failed again the past two years because of "a major disruption of the normal upwelling pattern."

"But this year is very different," he said.

Because of the plentiful krill, the juvenile rockfish that seabirds eat are more abundant. The auklets are having their best reproductive year in a long time - much more in the normal range.

The number of brown pelicans has also increased. The population had crashed due to eggshell thinning before the pesticide DDT was banned in America in 1972, but has been recovering ever since, and this year the number of brown pelicans has reached a new peak, Bradley reported. His census on South Farallon Island alone last month counted 5,856 pelicans roosting there, a new high, he said.

"Still, there are anomalies we can't explain," Bradley said. "The numbers of Brandt's cormorants, for example, which should normally be chowing down on this year's abundant anchovies, haven't recovered. It's really a mystery, and we don't have an answer for it."

From his perch on the Farallones, Bradley can survey the ocean as far as the horizon, and this year, he said, he is seeing far more humpback whales than he has in many years. "They're going where the krill is," he said, "and there's plenty of that this year."